Controller inserting only last data in array into database - laravel-4

Question

Have asked this question before but it wasn't answered.So am asking again.I have a table subjects with columns:
id->primary key,auto-increment;
class_id->foreign key->refrences id on classes table;
subject;
and a users table:
id->primary key,auto-increment;
username;
password;
and a classes table:
id->primary,autoincrement;
class;
term;
and a pivot table student_user:
id->primary;
user_id->refrences id on users table;
subject_id->refrences id on subject table;
class_id->foreign,refrences id on classes table;
And i have my model to define there relationship thus
//User Model
//User.php
public function subjects()
{
return $this->belongsToMany('Subject');
}
public function myclass()
{
return $this->belongsTo('SchoolClass');
}
//Class Model
//SchoolClass.php
public function subjects()
{
return $this->hasMany('Subject','class_id');
}
//Subject Model
//Subject.php
public function term()
{
return $this->belongsTo('SchoolClass');
}
public function student()
{
return $this->belongsToMany('User');
}
Now here comes the problem.When ever i try to insert data into the pivot table subject_user,only the the last data in the array of values that i want to insert gets saved into the database.I dont know if its the foreign constraint keys that's only updating the row instead of inserting a new one when looping through data.I cant figure out what is wrong.And below is my controller to see how my data is been inserted.Am not very conversant with relationships in laravel
//Save Registered Courses
public function post_proceed_registration()
{
$PageTitle = 'Register Subjects';
$id = Auth::user()->id;
$User = User::find($id);
$class_id = $User->profile->class_id;
$subjects = Input::get('subjects');
$registration = RegistrationCheck::where('class_id',$class_id)->where('user_id',$id)->pluck('status');
if(count(Input::get('students')) != 0)
{
if($registration == 'true')
{
PivotSubject::where('user_id',$id)->where('class_id',$class_id)->delete();
foreach($subjects as $sub_id)
{
$subject = new PivotSubject;
$subject->user_id = $id;
$subject->subject_id = $sub_id;
$subject->class_id = $class_id;
$subject->save();
}
RegistrationCheck::where('class_id',$class_id)->where('user_id',$id)->update(['status'=>'false']);
return Response::Json('Success: Subject/Courses Registered');
}
return Response::Json('Error: You already registered for this Term/Semester.Please Contact ICT for help');
}
return Response::Json('Error:You did not choose any course to register');
}
Am stucked here.Any help would be appriciated